Answer 1

Activity depends on your task.
Here parent, child relation is deferent compare to package..
See :
package myne;
class A{
..
}
class B {
..
}
If define another class seaparately , add same name package

package myne;
class C
{
..
}

Now all 3 classes belong to same package..
You can just import
import myne;
Then use A, B, C classes..

Answer 2

You have to import classes using import

For example:

import example.Abc;

Here example is s package and Abc is a class

Answer 3

* Package creation *

create package grouping related class in one folder. Then import.

Answer 4

Concept is package in Java.
It's creation, using by import.

edit :
BurningHeart
https://www.javatpoint.com/package

in eclipse, you just add package name at first name for all related classes..
for example : for your mentioned classes, add package name ex :
package mypackage ; // as a first line for those 3 classes.. your job is done. in IDEs , you don't need other steps mostly.....